cichlidaholic said:
I've actually known of hobbyist who had never churned their sand before, then gone to rearrange things or change substrate and lost alot of fish.
I've also heard this claim more than once, but I believe it's more likely due to an ammonia spike from moving waste and leftover food, more so than any effects of anaerobic gases. Sulfur Dioxide (SO
2) cannot penetrate water, it's self contained in the bubbles that raise to the surface. This is why they smell like rotten eggs.
I'll try and paraphrase some information on this debate. This is from memory and Wikipedia so if there's any chemists out there who can correct me, please chime in!
In order for Sulfur Dioxide to have any effect in water, it needs to go through a complex process called the "contact process" so that it's converted to Sulfur Trioxide. It can then be introduced to water which in turn, produces sulfuric acid. The contact process can't take place in water alone. The sulfur dioxide won't interact with H2O and so it simply rises to the top and dissipates into the air.
The only way that it
may have an effect on fish, is if a bubble rising to the top, happens to pass through the gills of fish, which is unlikely.